Metal filters have long been used for a variety of applications. For example, porous stainless steel filters prepared from sintered metal particulate, e.g., stainless steel powder, have found use in a variety of processes where high pressure drops are acceptable and in applications where relatively fine filtration capability must be combined with mechanical strength, resistance to high temperatures and/or resistance to chemical attack. Such applications include the filtration of fine catalysts used in fluidized bed catalytic processes where elevated temperatures are encountered, e.g., fluid cat cracking, and in the manufacture of high fidelity recording tapes. Still another use of such filters is in the filtration of molten resin used in the manufacture of polymeric films and fibers as, for example, polyester film.
One form of commercially available metal filters in cylindrical form is typically prepared from sheet material which is formed into a cylindrical shape and then longitudinally welded. Unfortunately, this method of manufacture results in a structure sensitive to rapid temperature change, i.e., uneven heating and cooling can ultimately result in cracking and failure of the structure adjacent the seam weld. Other drawbacks to such welded structures are nonuniform blow back characteristics and the inability to make relatively small diameter structures, e.g., at one-half inch diameter, the welded seam occupies a significant portion of the overall surface available for filtration, limiting the onstream filter life for a given cycle.